This disclosure relates to a turbine blade rotor assembly. In particular, the disclosure relates to an assembly for which a platform adjacent to the turbine blade is provided by a separate structure.
Typical turbine blades for a gas turbine engine are constructed from a nickel alloy. Multiple turbine blades are arranged circumferentially about a rotor and secured thereto by their roots. Typically, turbine blades include integral platforms extending circumferentially from both the high and low pressure sides of the airfoil near the root. The platforms act as flow guides that divert airflow along a desired flow path.
It is desirable to increase turbine rotor speed to improve the performance and efficiency of gas turbine engines. The turbine rotor speed is limited by the loads on the turbine blades. In particular, the turbine blades, which are typically constructed from nickel alloy, speed can be limited by the attached platforms, which curl and crack under loads.
In an effort to reduce turbine blade cooling flows, it has been suggested that turbine blades could be constructed from a ceramic matrix composite (CMC). This design approach endeavored to eliminate the use of nickel in the turbine blade and substitute a high temperature CMC. The layered construction of the CMC blade favors a direct connection between the attachment feature and the airfoil itself. To simplify the construction, the platforms are provided by separate structure that is secured to the rotor because providing an integral platform to a CMC blade is very difficult.
The current state of the art cooling schemes for nickel alloy blade have improved the thermal capability such that alternative material such as CMC may not offer significant benefits. However, the problem of blade platform capability remains. Thus, it is desirable to utilize a nickel alloy blade that does not have platforms that crack at increased turbine rotor speeds.